Re: [PATCH v7] scsi: ufs: add ioctl interface for query request

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Mar 09, 2016 at 08:52:59PM -0000, ygardi@codeaurora.org wrote:
> > On Wed, Mar 09, 2016 at 07:09:49PM -0000, ygardi@codeaurora.org wrote:
> >> > On Wed, Mar 09, 2016 at 04:11:33PM +0200, Yaniv Gardi wrote:
> >> >> This patch exposes the ioctl interface for UFS driver via SCSI device
> >> >> ioctl interface. As of now UFS driver would provide the ioctl for
> >> query
> >> >> interface to connected UFS device.
> >> >>
> >> >> Reviewed-by: Subhash Jadavani <subhashj@codeaurora.org>
> >> >> Signed-off-by: Dolev Raviv <draviv@codeaurora.org>
> >> >> Signed-off-by: Gilad Broner <gbroner@codeaurora.org>
> >> >> Signed-off-by: Yaniv Gardi <ygardi@codeaurora.org>
> >> >
> >> > What tool is going to use this ioctl?  Why does userspcae want to do
> >> > something "special" with UFS devices?  Shouldn't they just be treated
> >> > like any other normal block device?
> >> >
> >>
> >> Any userspace application can be a tool.
> >> We already implemented and used a user space application, that sent
> >> queries to the UFS devices in order to get information and descriptors.
> >
> > But do you want to do with that information?  Why does userspace care?
> >
> 
> i don't really understand the subtext of your question -
> as ANY ioctl cb, we decided to implement the ioctl callback of this scsi
> device in order to get information like UNIT DESC, DEVICE DESC, FLAGs,
> ATTRIBUTES.
> When dealing with UFS devices, one should be able to read the
> characteristics of the device. why ? well, why not ?

Why aren't those characteristics just exported as sysfs attributes under
control by the UFS controller driver?  Why do you need/want an ioctl for
this?

> during development of this driver, it was useful in many cases to be able
> to communicate with the device, by simple IOCTL command, rather than
> implementing ad-hock.

Do other storage busses have these types of "custom" ioctls for their
bus-type alone?  For simple attributes like this, shouldn't you be using
sysfs instead so that it is much easier for userspace tools to get
access to them?

thanks,

greg k-h